import math

x1,x2,x3,x4 = map(float, input().split())
n = (x3 - x1)**2 + (x4 - x2)**2
ans = math.sqrt(n)
print(ans) import math math x1,x2,x3,x4 = map(float, input().split()) x1 map(float, input().split()) map float input().split() ().split () input split x2 x3 x4 n = (x3 - x1)**2 + (x4 - x2)**2 n (x3 - x1)**2 + (x4 - x2)**2 (x3 - x1)**2 x3 - x1 x3 x1 2 (x4 - x2)**2 x4 - x2 x4 x2 2 ans = math.sqrt(n) ans math.sqrt(n) math.sqrt math sqrt n print(ans) print ans x3,x4 = map(float, input().split()) map(float, input().split()) x3 n = (x3 - x1)**2 + (x4 - x2)**2 (x3 - x1)**2 + (x4 - x2)**2 n ans = math.sqrt(n) math.sqrt(n) ans x1,x2,x3,x4 = map(float, input().split()) map(float, input().split()) x1 x2,x3,x4 = map(float, input().split()) map(float, input().split()) x2 x4 = map(float, input().split()) map(float, input().split()) x4
import math

x1,x2,x3,x4 = map(float, input().split())
n = (x3 - x1)**2 + (x4 - x2)**2
ans = math.sqrt(n)
print(ans)
